Surveying is as old as the art of civil engineering itself and predates even recorded history. One of the primary objectives of surveying is accuracy and precision in measurements made. In measuring an elevation, for example, a calibrated reference is placed at a point of interest while a scope is placed at a second point of reference. The second point of reference, and thus the scope, has a known elevation. The scope is leveled and aimed at the calibrated reference. A horizontal reference line is positioned within the view through the scope such that visual comparison of the reference line as viewed through the scope to the calibrated reference provides a measurement of the difference in elevation between the first and second points of interest.
At times, the distance between the first and second points of reference is considerable and accurate optical comparison between the reference line and the calibrated reference is difficult. For example, conventional calibration systems mark centimeters and perhaps half centimeters such that millimeters are merely estimated by a surveyor. Despite high quality optical magnification within the scope, comparison of the reference line within the scope to marked half-centimeters to estimate a measurement to the nearest millimeter is quite difficult. However, simply marking the calibrated reference with reference marks spaced by one millimeter is ineffective. Specifically, reference marks so close to one another appear as a single, indistinguishable mark from a distance notwithstanding high quality optical magnification.
Another problem with current surveying calibration references is that the view of the scope frequent has insufficient information to make a complete assessment of a current measurement. For example, it is common that only half-centimeter marks of the calibrated reference are visible through the scope at a particular measurement. Such generally requires that the scope be panned up and/or down to view markings which indicate absolute measurements such that the relation between the originally viewed half-centimeter marks and the absolute measurement markings can be determined. Only then can a measurement be made by comparison of the reference line to the half-centimeter marks which would otherwise lack context.
What is needed is a calibration system by which more precise and accurate measurements can be made and by which such measurements can be made without reference to distant portions of a calibrated reference.